Electro-mechanical actuators are commonly used for a wide variety of applications. In an automotive setting, for example, actuators may be used for raising and lowering windows, for opening and closing sunroofs, controlling windshield wipers, etc. In a power window application, for example, an actuator may be located in each door assembly having an operable window, and usually includes an electric motor of some sort and a drive mechanism for raising and lowering the window, or in the case of the sunroof, for example, for opening and closing, or otherwise moving the sunroof.
Power windows, sunroofs, etc. are conventionally driven by a single motor, which may be gear driven or of a worm gear configuration, connected to a mechanism for raising and lowering the window, operated by means of a switch control. Such an actuator is disclosed, for example, in U.S. Pat. No. 5,801,501, wherein a single motor drives a worm gear drivably connected to mechanism for lifting the window or moving the sunroof. This configuration transmits all torque from a single motor. The higher friction and lower efficiency worm drive results in lower overall system efficiency, and greater electrical power requirements to achieve sufficient power output.
Such single motors are often larger in size than may be desirable from an overall design standpoint and may require a comparatively large amount of electric current in order to function smoothly, efficiently, and responsively. U.S. Pat. No. 5,787,644, for example, discloses a power window system with the drive motor located within the body rather than within the door of the vehicle due to the size of the motor. Although this alleviates, in part, the design concerns, the problems associated with engine size and power requirements remain.
Utilizing a smaller motor, however, sacrifices motor power, speed and efficiency. Moreover, if the motor fails, the window, sunroof, wiper, etc., as the case may be, is rendered inoperable, whether in open or closed position. Not only are such failures common, they occur without any prior notice. U.S. Pat. No. 5,024,022 addressed these issues by providing an automobile window opening and closing device which has a manually operated mechanism and a power-operated mechanism in combination. This configuration, however, represents a step backwards from the full power window or sunroof features desired in today's automobiles.
An application that uses two motors is found in a device for automatically adjusting a rearview mirror, U.S. Pat. No. 4,815,837. There, each electric motor operates a separate drive mechanism for performing a distinct adjustment of the angles of the mirror. U.S. Pat. No. 5,336,045 discloses an electrically powered linear actuator for supporting and moving the cabin of a fight simulator, including two large motors capable of moving and supporting the substantial weight of the simulator, each having a pinion engaging a chain or gear train coupling, which drives a pulley secured to the end of a screw threaded drive shaft driving a traveling member.
There is therefore a need in the art for an efficient and cost-effective actuator to design that overcomes the deficiencies of the prior art.